The present invention relates generally to wood product fabrication and more particularly to the fabrication of wooden pallets.
Wooden pallets for transporting and storing goods are widely used in commerce and industry, and are particularly adapted to be handled by fork lift type handling equipment. A typical pallet is constructed by nailing a series of deck boards to a supporting base of transversely positioned, spaced apart stringers. The deck boards form a load supporting surface upon which goods to be transported are placed. A pallet may have deck boards nailed to only one side of the transversely positioned stringers, but customarily they are nailed to both sides.
Attempts have been made to automate various aspects of the pallet fabrication process. For example, in U.S. Pat. No. 5,095,605 to Tonus, the automatic nailing of deck boards to stringers is described. In U.S. Pat. No. 3,706,408 to Burch, the automatic feeding of deck boards and stringers to a pallet assembly area are described.
Typically, stringers are pre-cut and stacked into arrays and placed within close proximity of pallet fabrication devices. These stringers are typically manually unloaded from these stacked arrays and placed within various feeder devices which automatically position them for assembly. It would be desirable to automate the handling of stringers such that multiple stringers could be moved simultaneously into the feeding devices. Unfortunately, the slender nature of stringers makes handling via automatic devices somewhat difficult. Also, the stringers have a tendency to bind up when pushed in groups.
Attempts to automate the step of nailing the deck boards and stringers together have primarily focused on the use of hydraulically operated nailing devices and on the use of xe2x80x9ccollatedxe2x80x9d nails (i.e., nails that are packaged and presented to the nailing device in an interconnected fashion). Unfortunately, hydraulically operated nailing devices have several drawbacks. The nailing speed of a hydraulically operated ram often requires the nailing device to pause briefly each time a nail is to be driven into a deck board and stringer. As a result, pallet production rates are somewhat limited. In addition, hydraulically operated nailing stations use hydraulic fluid, which can be somewhat messy and require a certain amount of maintenance to avoid leaks.
Attempts to automate the nailing of deck boards to stringers have typically utilized collated nails as opposed to bulk nails because collated nails are typically easier to handle at high speeds than are bulk nails. Another reason collated nails have been favored is that controlling the delivery of bulk nails to a nailing station operating at high production speeds has proven somewhat difficult. Unfortunately, the cost of collated nails is often several times that of bulk nails.
Automatic nailing devices often move along a frame via a gantry and are configured to drive nails into pallets located thereunder. Unfortunately, the nailing operation is a somewhat violent and jarring operation that can cause the gantry to xe2x80x9crackxe2x80x9d relative to the pallet and become misaligned. This can reduce accuracy of nailing. Downtime for gantry realignment is detrimental to production rates for these automatic nailing devices.
In view of the foregoing, it is an object of the present invention to provide an automatic pallet fabrication apparatus that eliminates the problems associated with nail driving systems that can utilize bulk nails.
It is also an object of the present invention to provide such an apparatus that utilizes bulk nails.
It is another object of the present invention to provide an automatic pallet fabrication apparatus including an automatic stringer feeding system that can move multiple stringers simultaneously.
It is a further object of the present invention to provide an automatic pallet fabrication apparatus including an automatic nailing system that resists misalignment during operation.
These and other objects are accomplished, according to the present invention, by an apparatus for making pallets which includes an automatic stringer feeding system, an automatic stringer advancing system, a pallet assembly station, a nail delivery system, and a pallet stacking system. Wood stringers are automatically fed to a series of hoppers which facilitate advancing the stringers into the pallet assembly station. Spaced apart deck boards are nailed, via the nail delivery system, to both sides of the supporting base of transversely positioned stringers in the pallet assembly station. Assembled pallets are removed from the apparatus and stacked for use or shipping.
According to one aspect of the present invention, a longitudinally extending frame includes a first pallet assembly area. A gantry, movable along the longitudinally extending frame on generally parallel spaced apart linear guide bearings, includes multiple nailing stations in adjacent spaced relationship. Each of the nailing stations includes a pneumatically driven double ram for nailing together stringers and overlying deck boards positioned within the first pallet assembly area.
In operation, an operator places deck boards transversely across the spaced apart stringers which are automatically fed into the first pallet assembly area from the elongated storage hoppers. The gantry passes continuously over the first pallet assembly area and nails are driven into the underlying deck boards and stringers to form a half-assembled pallet. The gantry reverses its direction and the half-assembled pallet is flipped over into a second pallet assembly area adjacent the first pallet assembly area.
Stringers are advanced automatically from the hoppers into the first pallet assembly area. An elongated bar is configured to push the lowermost stringer in a stack endwise from each respective hopper to the first pallet assembly area. An operator then places deck boards transversely across the stringers in the first pallet assembly area and across the inverted stringers in the second pallet assembly area. The gantry reverses its direction and passes continuously over the second and first pallet assembly areas. Nails are driven into the underlying deck boards and stringers to form a completely-assembled pallet in the second pallet assembly area and a half-assembled pallet in the first pallet assembly area. The gantry reverses its direction and the half-assembled pallet is flipped over into the second pallet assembly area and the completely-assembled pallet is pushed from the second pallet assembly area to a stacking area.
According to another aspect of the present invention, the elongated hoppers are positioned adjacent the first pallet assembly area and are arranged in substantially parallel spaced relationship. Each of the hoppers is configured to hold multiple elongated stringers in an upright stack wherein the stringers are oriented in a substantially horizontal edgewise configuration. Each hopper has a sensor for detecting stringer stack height within the hopper. The sensor is positioned to detect the endwise face height of the stringers within the hopper.
According to another aspect of the present invention, an automatic stringer loading system is provided for loading stringers into each of the hoppers. The hopper loading system is operatively coupled to the sensors on each hopper such that when stack height in a hopper is below a predetermined height, the stringers are automatically loaded into the hopper.
Stringers are provided initially in a stacked array such that the longitudinal axes of the stringers are generally parallel. The hopper loading system includes a first conveying system for conveying a layer of stringers from the stacked array in adjacent substantially horizontal relation along a first direction. An elevating system is provided for elevating the stacked array of stringers to the first conveying system to facilitate removing a stringers from the array one layer at a time.
The hopper loading system also includes a second conveying system for conveying stringers in adjacent substantially horizontal relation to each hopper along a second direction substantially transverse to the first direction. The first and second conveying systems each include at least one elongated bar configured to push the stringers along the respective first and second directions. The first and second conveying systems are operatively coupled such that the first conveying system conveys stringers along the first direction in response to the second conveying system conveying stringers along the second direction.
According to another aspect of the present invention, a gantry position control system is provided for controlling the continuous movement of the gantry along the longitudinally extending frame. A nailing station actuation system operatively coupled with the gantry position control system is provided for causing each of the pneumatically driven rams to nail together underlying deck boards and stringers as the gantry moves continuously along the longitudinally extending frame.
Each bulk nail retaining bin includes a slotted ramp leading from the receiving slot to a respective nailing station. The slotted ramp is configured to deliver nails in a single row to the nailing station. The slotted ramp includes an inclined portion, a flattened end portion adjacent the nailing station, and an arcuate transitional portion between the inclined and flattened end portions. A plurality of retractable pins positioned at the flattened end portion transversely to the slot control entry of each nail into the magnetic chuck. The pins separate the leading nail in the row from the remaining nails in the row.
According to another aspect of the present invention, each nailing station includes a magnetic chuck for receiving a nail from a respective slotted ramp and for holding a nail in position for nailing by the pneumatically driven ram. The magnetic chuck may include at least one rare earth magnet.
According to another aspect of the present invention, a method of making pallets includes conveying a plurality of elongated stringers in adjacent substantially horizontal relation along a first direction, and conveying the elongated stringers in adjacent substantially horizontal relation along a second direction to a hopper. The second direction may be substantially transverse to the first direction. The first direction is generally parallel with a longitudinal axis of each of the elongated stringers.
The present invention is advantageous in that an improved rate of pallet production can be achieved as compared with existing methods of production. The automatic stringer feeding system of the present invention is advantageous over existing stringer handling techniques because the process of pushing multiple stringers along their endwise faces reduces the likelihood of the stringers becoming dislocated.
The use of a dedicated bulk nail supply bowl and delivery system to each nailing station permits increased nail capacity and decreased downtime to resupply nails as compared with systems utilizing single supply bowls. Furthermore, the use of a dedicated bulk nail supply bowl to each nailing station also simplifies the delivery of nails in that delivery is not coordinated between multiple nailing stations.
The pneumatic nailing station of the present invention is advantageous over prior pallet nailing systems in that it can handle bulk nails. Prior systems could not easily handle bulk nails but could handle collated nails. Prior systems were not able to feed and hold bulk nails as quickly as the present invention. Pneumatically driven nailing rams are typically faster than hydraulically driven nailing rams and do not require the nailing gantry to stop at each location where a nail is to be driven into the pallet. As such the nailing gantry can move along its path of travel without pausing, thereby increasing the rate of pallet production.